Gas turbine engines include compressor rotors having a plurality of rotating compressor blades. Minimizing the leakage of air, such as between tips of rotating blades and a casing for a gas turbine engine, increases the efficiency of the gas turbine engine because the leakage of air over the tips of the blades can cause aerodynamic efficiency losses. To minimize this, the gap at tips of the blades is set small and, at certain conditions, the blade tips may rub against and engage in an abradable seal at the casing of the engine. The abradability of the seal material prevents damage to the blades while the seal material itself wears to generate an optimized mating surface and thus reduce the leakage of air.
Desirable features of an abradable seal include low gas permeability, low roughness, and sufficient erosion resistance to generally maintain dimensions over time while remaining abradable during interaction with blades. These factors give rise to abradable seals which are hard, dense, and formed from abrasive blade tip treatments. These treatments are costly. In addition, as compressor exit temperatures climb substantially above 1000° F. (538° C.), the thermally grown oxides within the abradable coatings begin to thicken, which may cause excessive wear to bare blade tips. Thus, there is a continued need in the art for improved abrasive blade tip treatments in modern engines.